This invention relates to electronic systems such as computers, wherein certain components maybe mounted on a large number of generally similar printed circuit boards or cards arranged to be plugged in corresponding pin plates or plugs on a chassis. More particularly, the invention resides in a modified circuit card extender which provides circuit card keying and mating alignment pins, thus bringing out the electrical connections of a particular printed circuit card or board outside the chassis area for easy access for testing and repair.
In electronic systems such as a computer which use keyed printed circuit cards or boards, quick trouble shooting of a malfunctioning circuit card is quite important and the use of keyed circuit cards in such systems is quite common. However, no provisions are usually made for transmitting the card keying along the electrical connections along the body of a circuit card extender which is used for bringing out the electrical connections out in a more convenient place than the congested area where the particular circuit card board is located in the circuit. It is usually desirable that a circuit card extender must be universal, and be able to accept any circuit card and be acceptable by any location on the chassis. This is commonly accomplished by having no keying arrangement at all on the circuit card extender, or by having a universal fixed or rotatable key arrangement on the extender portion which mates with the pin plate or chassis connections but has no correlation with the portion of the circuit card extender which meets with the printed circuit card or board. Where no keying is provided at all, the extender configuration will allow any circuit card or board to be inserted into any chassis location, which defeats the purpose of card keying to prevent any damage to electrical equipment by inadvertently plugging the wrong circuit card into the plug or connector for specific card or board on the chassis. Another disadvantage of such a system is that without the keying pins on the card extender body, chassis mating alignment which is secondary function of these keys is lost, thereby allowing bending of electrical pins due to misalignment of high density mating connections. In the case where some sort of keying is provided only at the card extender interface with the chassis, the alignment problem is solved but the problem of inserting an incorrect circuit card or board into a given location is still possible. Furthermore, due to the small size and space limitations usually imposed by the system configuration, this type of arrangement is prone to damage or breakage. Both types of extenders are thus unsatisfactory as they permit expensive and extensive damage to electronic systems during testing and trouble-shooting when circuit card extenders are used.